The present invention generally relates to video signal digital processing systems, and more particularly to a video signal digital processing system in which a video signal is sampled at a sampling frequency which is in a predetermined relationship with a horizontal synchronizing signal frequency of the video signal so that the video signal can be processed digitally by use of a simple circuit. The same circuit can be used to digitally process the video signal regardless of whether the video signal employs the NTSC system or the PAL system.
A video signal processing circuit is used in a television receiver, a video tape recorder, and the like. A conventional processing circuit processes a video signal in the analog form, and for this reason, a large number of circuit elements such as capacitors, resistors, and coils are used and the circuit elements require adjustments. Accordingly, the conventional processing circuit is relatively expensive, and the productivity of the processing circuit is poor because the circuit elements require adjustments. Hence, there were demands to reduce the number of circuit elements of the processing circuit and to make it unnecessary to adjust the circuit elements. As a method of meeting such demands, there is the method of processing the video signal digitally.
However, the existing television broadcasting systems can be roughly divided into the NTSC system, the PAL system, and the SECAM system. Hence, it is necessary to independently prepare a digital processing circuit for digitally processing the video signal for each of the three television systems. However, the NTSC system and the PAL system are similar to some extent, and with respect to the luminance signal, there are no substantial differences between the two systems except for the frequency band of the luminance signal. Therefore, if the chrominance signal of the NTSC system video signal and the chrominance signal of the PAL system video signal can be processed in the same chrominance signal processing circuit, it becomes possible to process the NTSC video signal and the PAL system video signal in the same digital processing circuit, and the effects obtained would be great. In other words, it becomes unnecessary to independently design the digital processing circuit for the NTSC system and the PAL system, and the manufacturing cost of the digital processing circuit can be kept down to a minimum since the same digital processing circuit can be used in common for processing the NTSC system video signal and the PAL system video signal.